We are continuing our studies of template-directed syntheses in aqueous solution. We have devised a special dialysis apparatus in which it is possible to study the elongation of oligonucleotide primers in the presence of an activated mononucleotide and then to remove the mononucleotide once it has undergone hydrolysis. In this way we are able to supply new activated intermediates repeatedly without losing any oligonucleotide products that are formed. We hope to demonstrate the template-directed synthesis of oligonucleotides containing up to 20 residues. We are also developing a series of activated nucleotides in which the P atom of the nucleotide is joined to the N atom of polyamine, such as spermine. We hope that by using these reagents we will be able to incorporate pyrimidines into oligonucleotides on a polypurine template. Another aspect of our work will be concerned with the synthesis of nucleotide analogs and specifically-labelled nucleoside polyphosphates such as alpha, beta, and gamma ATP.